1. Field of the Invention
The present invention relates to electronic control circuit, and more particularly to a circuit for controlling the mixing of two signals of differing frequencies.
2. Description of the Prior Art
In a number of instances it is desirable to have means for controlling an output device at different frequencies during alternate periods. In the prior art, there have been provided circuit schemes for accomplishing interleaving of signals of different wave forms. An example of such a patent is Patrickson U.S. Pat. No. 3,657,558 wherein ramp generators are alternately triggered into operation to provide interleaved signals of different slope and duration. These are interleaved individual pulse signals.
In certain recording fields, for example in the area of recording certain medical data, it is highly desirable to have the facility for recording several different types of data on the same record member. In at least one such application, one type of data to be recorded is of necessity a relatively slow response type signal. In recording a plurality of different type signals substantially simultaneously on the same record member it is the usual practice to multiplex the several signals for application to the control of the recording instrumentality which may, for example, be a cathode ray tube type recording device. If the multiplexing and data sampling occur at the rate determined by the slowest response type signal, it is quite probable that significant data changes in the faster response type signals will be lost. An example of such a multiple data recording instrumentality is seen in an instrument which responds to and records signals both from an ultrasound scanner and from body function detectors such as electrocardiograph sensors. As is known in the art, the ultrasound scanner is a device which responds to sonic type waves to provide an echo signal imaging of body elements and constitute relatively slow response type signals. On the other hand, signals representative of electrocardiograph data include high frequency components which, if they are sampled at the slower rate of the echo signals would tend to lose substantial definition. In order to properly record both the echo data and the electrocardiograph data it would be necessary to have sampling control signals of lower frequency to control the sampling and scanning of the echo signals and a higher frequency control signal for controlling the sampling and scanning of the electrocardiogram signals. The interleaving of single pulse signals of different wave forms such as that shown in the aforementioned Patrickson patent would not provide the necessary control signals for this application.